Fuel injection valve and direct injection engine using the same

ABSTRACT

The invention provides for a fuel injection valve for a direct gasoline injection engine, a direct injection engine and an automobile using the same, which can prevent the deposits produced during combustion of gasoline from accumulating on the surface of the fuel injection valve, or easily remove the deposits therefrom. A reaction-bonded layer of perfluoropolyether compounds having alkoxy silane as its terminal group is provided on the surface of the fuel injection valve of the invention.

FIELD OF THE INVENTION

The present invention relates to a novel fuel injection valve for adirect injection engine, and in particular, it relates to a fuelinjection valve and a direct injection type engine using the same for anautomobile.

DESCRIPTION OF RELATED ART

A gasoline direct injection engine is comprised of a cylinder block, apiston having a piston ring, which is inserted in the cylinder block,and a cylinder head which is in the upper portion of the cylinder block.A combustion chamber is formed in a space surrounded by an internal wallof the cylinder block, an upper surface of the piston and a bottomsurface of the cylinder head. Substantially in the center portion of thecylinder head, there is mounted an ignition plug. An air-intake valveand an exhaust valve are provided near the ignition plug. In addition, afuel injection valve 1 is provided for directly injecting fuel into thecombustion chamber. Atomized fuel injected from the fuel injection valve1 impinges on a concave surface at the top of the piston to be reflectedand guided toward the vicinity of the ignition plug which issubstantially in the center portion of the cylinder head, wherebyrealizing a stratified lean burn combustion is realized.

The fuel injection valve of the gasoline direct injection engine, whichis installed within the engine cylinder, is exposed to a hightemperature combustion gas. In this condition, deposits produced bycombustion of gasoline tend easily to accumulate on the tip of the fuelinjection valve, thereby distorting a fuel atomization pattern specifiedto take place within the engine cylinder, consequently resulting in adecrease of its fuel flow rate, and deterioration of a fuel-air mixture,thereby causing its combustion to become very unstable. A cause of thedeposits is considered to be due to accumulation of soot produced in thecombustion chamber, and a gumlike substance produced by thermaldecomposition of gasoline. In particular, when the temperature in thecircumference of the fuel injection valve is higher than 160° C., thedeposits are reported to be easily accumulated. Several methods havebeen tried for cleaning such deposits by mixing additives into gasolineor by reducing the coarseness of the surface of the fuel injection valve(Jidosha-gijyutsu-kai; symposium preprint 976 (1997-10)). Further, manyattempts have been made to drop the temperature of the tip end of theinjection valve as disclosed in JPA Laid-Open No. 9-264232. However, ithas been difficult by any of these attempts effectively to reduce thedeposits. JPA Laid-Open No.9-264232 discloses that the surface of thefuel injection valve is made oleophobic so as to be able easily toremove the deposits, and prevent the decrease of fuel flow. According tothis method, a fluoroalkyl compound is reaction-bonded on the surface ofthe fuel injection valve so as to make its surface oleophobic. Stillfurther, according to JPA Laid-Open No. 7-246365, it is disclosed thatthe surface of the fuel injection valve is treated by a sol-gel methodusing a mixture solution of a metal alkoxide and a fluoroalkyl groupsubstituted metal alkoxide which is prepared by substituting a part ofalkoxyl group with a fluoroalkyl group, thereby making the surface ofthe fuel injection valve oleophobic such that the deposits can be easilyremoved and the decrease in the fuel flow can be prevented. This methodincludes such one whereby a mixture solution of a fluoroalkyl groupsubstituted metal alkoxid compound and a metal alkoxide isreaction-bonded on the surface of the fuel injection valve so as to makeits surface oleophobic, and such ones to form various films as disclosedin JUP Nos. 55-116875 and 56-25067. However, these methods areaccompanied with a problem to be solved that when the temperature at thetip end of the fuel injection valve exceeds a point at which 90% of thefuel used evaporates, accumulation of deposits progresses on the fuelinjection valve so as to reduce the area of opening of the fuelinjection valve's port, thereby decreasing the flow rate of the fuel.

SUMMARY OF THE INVENTION

The cause of the production of the deposits is considered, as describedin JPA Laid-Open No. 9-264232, to be that high residual components inthe fuel tend to remain on the surface of the fuel injection valve, andits residual as a core causes subsequent dehydrogenation andpolymerization reactions. The prior art method of reaction-bonding thefluoroalkyl compound on the surface of the fuel injection valve so as tobe able easily to peel off the deposits is involved with the problemthat when the temperature at the tip end of the fuel injection valve israised as high as to increase the production of the deposits, its effectis reduced.

Further, the method disclosed in JPA Laid-Open No. 7-246365 whereby themixture of the metal alkoxide and the fluoroalkyl group substitutedmetal alkoxide was baked on the surface of the fuel injection valve soas to render the surface of the injection valve oleophobic therebyimproving its deposit peel-off capability, is associated with a problemthat when the temperature at the tip end of the injection valve israised and the production of the deposits increases accordingly, itsoverall effect is reduced. This cause is considered, as discussed in JPALaid-Open No. 10-159687, to be that the provision of the oleophobicproperty was insufficient to realize its designed function. Stillfurther, it is necessary for this oleophobic property to exist stably inconditions of a high fuel pressure, high combustion pressure, and highsurface temperatures of 150 to 200° C. on the surface of the injectionvalve.

In order to solve the problems associated with the prior art, it iscontemplated effective to coat the surface of the fuel injection valvewith a fluorine film having a low surface energy, or to reaction-bond athick film thereon using a fluorine compound having a long chainaccording to the invention. By provision of such coating or film, thedeposits thereon can be cleaned out easily by the fuel of gasolinethereby advantageously preventing adhesion of the deposits thereon. Ifthis object of the invention is realized, a stable combustion patterndesignated for a highly reliable gasoline direct injection engine can beachieved. In order to accomplish the object of the invention, there arethe following problems to be solved.

A material suitable for this object must be able to exist stably on thesurface of the fuel injection valve under conditions of 5-12 MPa of fuelpressures, and 150-200° C. of temperatures on the surface of the fuelinjection valve, and in addition, must be able to provide a low surfaceenergy with the oleophobic property. Here, the stability (to existstably) refers to that the material must be nonflammable even if in anenvironment exposed to the combustion of gasoline for a long time,therefore requiring a high oxidation stability, thermal stability, andgasoline stability, as well as a high adhesion to the surface of thefuel injection valve. Thereby, these problems must have been solved.

The object of the invention is to provide for a fuel injection valve foruse in a gasoline direct injection engine, a gasoline direct injectionengine and an automobile using the same, which can prevent the depositproduced in the combustion of gasoline to settle on the surface of theinjection valve thereof, or which can easily remove the depositsattached thereon.

According to the feature of the invention, a fuel injection valvesuitable for use in a gasoline direct injection engine is provided,which can prevent adhesion of the deposit produced in the combustion ofgasoline on the surface of the injection valve, and/or easily remove thedeposit adhered thereto.

A material of a deposit-resistant film on the surface of the fuelinjection valve suitable for use in a gasoline direct injection enginemust be such one which can stably exist on the surface of the injectionvalve which is exposed to an environment of 5-12 MPa of fuel pressure,150-200° C. of temperatures on the surface of the valve under combustionof gasoline, and in addition, which can provide a low surface energy aswell as a strong adhesion to the injection valve under such environment.

A surface modifying reagent for forming the deposit-resistant film inorder for the same to be used in the aforementioned environment, must beessentially nonflammable thereby limiting its materials to be used. Anorganic compound which can withstand the above-mentioned environment ispreferably a perfluoro compound. This compound is most preferable as amaterial which can provide for a low surface energy, and is alsopreferable in the terms of oxidation stability, thermal stability andgasoline resistant stability as well. However, because of its lowsurface energy, the perfluoro compound has a weak adhesion with asubstrate. Hence, it becomes necessary to provide for a compound whichhas a group to combine with the terminal of the perfluoro compound whichbonds with the substrate by reaction. Further, the length of molecularchain in the fluoroalkyl compound used in the prior art is as small as 1nm or less, therefore, when the deposit is pressed against the surfaceof the injection valve under the fuel pressure of 5-12 MPa, the depositis easily caused to pierce through 1 nm thick film of perfluoroalkylcompound to get directly in contact with the surface body to bondtherewith. In order to solve this problem, it is contemplated accordingto the invention that if a thick film of a fluorine compound having along chain is provided, the adhesion of the deposit can be prevented.However, because the number of carbon in the perfluoro alkyl compoundsis generally from 14 to 16 in maximum, it is difficult to synthesize itscompound having an increased polymerization.

Hence, we noted to use a polymer of a perfluoropolyether compound as acandidate material which can be stably used in the above-mentionedenvironment. This perfluoropolyether compound is an average number ofmolecule weights from 2000 to 8000, and a shape of the compound islooklike yarn ball of more than 1.5 nm in average size (2×radius ofmolecule rotation). Then, if a dense film of coating of aperfluoropolyether compound can be formed, the surface of the fuelinjection valve can be coated 1.5 nm thick or more in average. Becausethe surface of the yarn ball of the above-mentioned perfluoropolyethercompound is covered by fluorine atoms, it has a low surface energy,thereby preventing adhesion of the deposits, or facilitating peel-off ofthe deposits. Further, when subjected to an external mechanicalpressure, the above-mentioned yarn ball is considered to function as abuffer film. According to this effect, even if the deposit is pressedagainst the surface of the fuel injection valve at pressures of 5-12 MPaof the fuel, the deposit is considered not to penetrate through thecoating of perfluoropolyether compound, thereby preventing its adhesionon the surface of the injection valve. In order for thisperfluoropolyether compound to be strongly bonded on the substrate, amost general method will be to provide for alkoxy silane bonded to itsterminal.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, aspects and embodiments of the presentinvention will be described in more detail with reference to thefollowing drawings, in which:

FIG. 1 is a schematic diagram of a gasoline direct injection engineaccording to the invention;

FIG. 2 is a schematic diagram of a fuel injection valve according to theinvention;

FIG. 3 shows a relationship between operation times (h) and fuel flowreduction rates (%) of the embodiments of the invention treated byperfluoropolyether compounds;

FIG. 4 shows a relationship between concentrations and film thicknessesof the perfluoropolyether compounds according to the invention;

FIG. 5 is a diagram showing flow reduction rates of respective fuelinjection valves of embodiments of the invention and comparisonexamples;

FIG. 6 is another diagram showing flow reduction rates of respectivefuel injection valves of embodiments of the invention and comparisonexamples;

FIG. 7 is still another diagram showing flow reduction rates ofrespective fuel injection valves of an embodiment of the invention and acomparison example;

FIG. 8 is a diagram showing flow reduction rates of fuel injectionvalves of another embodiment of the invention and a comparison example;

FIG. 9 is a diagram showing flow reduction rates of fuel injectionvalves of still another embodiment of the invention and a comparisonexample;

FIG. 10 is a diagram showing flow reduction rates of fuel injectionvalves of another embodiment of the invention and a comparison example;and

FIG. 11 is a schematic diagram of a gasoline direct injection engineaccording to another embodiment of the invention.

DESCRIPTION OF NUMERALS

1, 47 . . . fuel injection valve;

2 . . . fuel injection valve drive circuit;

3, 48 . . . ignition plug;

4, 46 . . . intake valve;

5, 50 . . . exhaust valve;

6 . . . intake port;

7 . . . exhaust port;

8, 45 . . . piston;

9 . . . electronic control unit;

10 . . . cylinder head;

11 . . . injection valve drive signal terminal;

12, 42 . . . three-way catalyst;

13 . . . NOx catalyst;

14 . . . combustion chamber;

22 . . . housing;

23 . . . core;

25 . . . coil;

26 . . . armature;

27 . . . valve unit;

29 . . . valve body;

31 . . . fuel injection port;

32 . . . valve sheet;

33 . . . needle valve;

35 . . . swirler;

40 . . . throttle actuator;

49 . . . intake flow sensor.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides for a fuel injection valve suitable foruse in a gasoline direct injection engine, wherein the surface of thefuel injection valve is coated by reaction-bonding with aperfluoropolyether group compound having alkoxy silane at its terminal,or with a perfluoropolyether compound which is reaction-bonded via anadhesion promotion layer so as to provide for a low surface energy tothe fuel injection valve for the gasoline direct injection engine,thereby preventing the deposit from accumulating on the surface of thefuel injection valve or easily removing the deposit having been attachedtherefrom.

Specific chain structures of such perfluoropolyether compounds mayinclude the following formulas such as KRYTOX available from E.I. duPont de Nemours & Co. (Inc.), DEMNUM from DAIKIN INDUSTRIES, LTD., andFOMBLIN from AUSIMONT, LTD.

KRYTOX: F(CF(CF₃)—CF₂—O—)_(n)—  (Comp.3)

DEMNUM: F(CF₂—CF₂—CF₂—O)_(n)—  (Comp.4)

FOMBLIN: F(CF₂—CF₂—O)_(x)(—CF₂—O—)—_(y)  (Comp.5)

or

—{(CF₂—CF₂—O—)_(x)—(—CF₂—O—)_(y)—}—,

wherein n≧12 (integer), x+y≧28, and x/y=0.5 to 2.0.

Examples of structures of perfluoropolyether compounds, in cases wheretheir chain structures are of KRYTOX and DEMNUM groups, include thefollowing compounds 6 to 27.

 F—(C₃F₆—O)_(m)—C₂F₄—CONH—C₂H₄—NH—C₃H₆—Si(CH₃)(O—CH₃)₂   (Comp. 6)

F—(C₃F₆—O)_(m)—C₂F₄—CONH—C₂H₄—NH—C₃H₆—Si(O—CH₃)₃   (Comp. 7)

F—(—C₃F₆—O—)_(m)—C₂F₄—CONH—C₃H₆—Si(O—C₂H₅)₃   (Comp. 8)

F—(—C₃F₆—O—)_(m)—C₂F₄—COO—C₃H₆—O—C₆—Si(O—CH₃)   (Comp. 9)

F—(—C₃F₆—O—)_(m)—C₂F₄—COO—CH (CH₃)—CH₂—O—C₃H₆—Si(O—CH₃)₃   (Comp. 10)

F—(—C₃F₆—O—)_(m)—C₂F₄—CH₂—O—C₃H₆—O—C₃H₆—Si(O—CH₃)₃   (Comp. 11)

F—(—C₃F₆—O—)_(m)—C₂F₄—COO—C₃H₆—Si(CH₃)(O—CH₃)₂   (Comp. 12)

F—(—C₃F₆—O—)_(m)—C₂F₄—CH₂—O—CH(CH₃)—CH₂—O—C₃H₆—Si(CH₃)(O—CH₃)₂   (Comp.13)

F—(—C₃F₆—O—)_(m)—C₂F₄—CH₂—O—C₃H₆—Si (CH₃)(O—CH₃)₂   (Comp. 14)

F—(—C₃F₆—O—)_(m)—C₂F₄—CH₂—O—C₃H₆—Si (O—CH₃)₃  (Comp. 15)

F—(—C₃F₆—O—)_(m)—C₂F₄—COO—C₃H₆—Si (O—CH₃)₃  (Comp. 16)

F—(—CF(CF₃)—CF₂—O—)_(n)—CF(CF₃)CONH—C₂H₄—NH—C₃H₆—Si(CH₃)(O—CH₃)₂  (Comp. 17)

F—(—CF(CF₃)—CF₂—O—)_(n)—CF(CF₃)—CONH—C₂H₄—NH—C₃H₆—Si(O—CH₃)₃  (Comp. 18)

F—(—CF(CF₃)—CF₂—O—)_(n)—CF(CF₃)—CONH—C₃H₆—Si (O—C₂H₅ )₃   (Comp. 19)

F—(—CF(CF₃)—CF₂—O—)_(n)—CF(CF₃)—COO—C₃H₆—O—C₃H₆—Si(O—CH₃)₃  (Comp. 20)

 F—(—CF(CF₃)—CF₂—O)_(n)—CF(CF₃)—COO—CH(—CH₃)—CH₂—O—C₃H₆—Si(O—CH₃)₃  (Comp. 21)

F—(—CF(CF₃)—CF₂—O—)_(n)—CF(CF₃)—CH₂—O—C₃H₆—O—C₃H₆—Si(O—CH₃)₃  (Comp. 22)

F—(—CF(CF₃)—CF₂—O—)_(n)—CF(CF₃)—COO—C₃H₆—O—C₃H₆—Si(CH₃)(O—CH₃)₂  (Comp.23)

F—(CF₃)—CF₂—O—)—CF(CF₃)—CH₂—O—CH(CH₃)—CH₂—O—C₃H₆—Si(CH₃)(O—CH₃)₂  (Comp.24)

F—(—CF(CF₃)—CF₂—O—)_(n)—CF(CF₃)—CH₂—O—C₃H₆—Si(CH₃)(O—CH₃)₂  (Comp. 25)

F—(—CF(CF₃)—CF₂—O—)_(n)—CF(CF₃)—CH₂—O—C₃H₆—Si(O—CH₃)₃  (Comp. 26)

F—(—CF(CF₃)—CF₂—O—)_(n)—CF(CF₃)—COO—C₃H₆—Si (O—CH₃)₃   (Comp. 27)

where, m=14 in average, and n=24 in average.

Specific examples of the perfluoropolyether compounds in case theirchain structures are of FOMBLIN include the following structures.

A—CF₂—{—(—CF₂—CF₂—O—)_(y)—}—CF₂—A  (Comp. 28)

B—CF₂—{—(—CF₂—CF₂—O—)_(y)—}—CF₂—B  (Comp. 29)

wherein, A is —CONH—CH₂CH₂CH₂—Si—(—OCH₂CH₃)₃, B is—CH₂O—CH₂CH₂CH₂—Si—(—OCH₃)₃, x=21 in average, and y=27 in average.

KRYTOX group: F(CF(CF₃)—CF₂—O—)_(n)—CF(CF₃)—Z—B,

DEMNUM group: F(CF₂—CF₂—CF₂—O)_(n)—CF₂—CF₂—Z—B,

FOMBLIN group: B—Z—C₂F₄—O—{(CF₂—CF₂—O)_(x)—(CF₂—O)_(y)}—C₂F₄—Z—B,

wherein n is an integer equal to 11 or greater, x+y≧18, x/y=0.5 to 2.0,Z is a connection group which includes an alkylane or amino group whichcontains at least one of amide, ester and methylenoxide. B is remaininggroup of alkoxy silane.

Examples of structures of perfluoropolyether compounds in case theirchain structures have a KRYTOX and a DEMNUM group include the followingcompounds.

F(—CF₂—CF₂—CF₂—O—)_(m)—C₂F₄—CONH—C₃H₆—Si(CH₃)(O—CH₃)₂   (Comp. 33)

F(—CF(CF₃)—CF₂—O—)—CF(CF₃)—CONH—C₂H₄—NH—C₃H₆—Si(CH₃)(O—CH₃)₂  (Comp. 34)

F(—CF(CF₃)—CF₂—O—)_(p)—CF(CF₃)—CONH—C₂H₄—NH—C₃H₆—Si(O—CH₃)₃  (Comp. 35)

F(—CF(CF₃)—CF₂—O—)_(p)—CF(CF₃)—CONH—C₃H₆—Si(O—C₂H₅)₃  (Comp. 36)

Examples of structures of perfluoropolyether compounds in case theirchain length structures have a FOMBLIN group include the followingstructures 37 to 40.

C—C₂F₄—O—{(CF₂—CF₂—O)_(x)—(CF₂—O)_(y)}—C₂F₄—C  (Comp. 37)

D—C₂F₄—O—{(CF₂—CF₂—O)_(x)—(CF₂—O)_(y)}—C₂F₄—D  (Comp. 38)

C——C₂F₄—O—{(CF₂—CF₂—O)_(j)—(CF₂—O)_(k)}—C₂F₄—C  (Comp. 39)

D—C₂F₄—O—{(CF₂—CF₂—O)_(j)—(CF₂—O)_(k)}—C₂F₄—D  (Comp. 40)

where, C is —CONH—CH₂CH₂CH₂—Si(—OCH₂CH₃)₃, D is—CH₂O—CH₂CH₂CH₂—Si(—OCH₃)₃, x=21 in average, y=27 in average, j=8 inaverage, and k=10 in average.

All of the perfluoropolyether compounds shown in compounds 6 to 40dissolve in perfluorohexane or perfluorobutylmethylether which is a kindof solvent having some fluorine atoms. The solvent is expressed asfluorine solvent in this paper. In order to form a film of either one ofthe above-mentioned perfluoropolyether compounds on the surface of thefuel injection valve, the fuel injection valve is immersed into asolution having the perfluoropolyether compounds dissolved into thefluorine solvent such as perfluorohexane or perfluoromethylether or thelike. Alternatively, the solution is dripped on the nozzle portion ofthe fuel injection valve. Then, they are heated at 150° C. for 10minutes. By heat treatment described above, alkoxysilane which is at theterminal group of perfluoropolyether compounds 6 to 40 is caused toreact with a hydroxyl group present on the surface of the fuel injectionvalve to bind together. By a simple process as described above, areaction film of the perfluoropolyether compound can be formed on thesurface of the fuel injection valve according to the invention. Athickness of a film to be formed thereon depends on a molecular weightand a concentration of coating of the perfluoropolyether compounds.Thermal stabilities and oxidation stabilities of respective reactionfilms obtained as above are found to have been improved. However,compounds 9, 10, 12, 16, 20, 21, 23 and 27 wherein their binding groupis ester are slightly inferior in these stabilities compared with theother perfluoropolyether compounds of the invention.

A most preferable method for stably bonding the perfluoropolyethercompounds 6 to 40 on the surface of the substrate is to use alkoxysilane as a reaction group. However, it is not limited thereto, andalkoxy titanium or akloxy zirconium may be used as well.

When there does not exist an adequate oxide film which provides for areaction site with respect to compounds 6-40 on the surface of the fuelinjection valve for the gasoline direct injection engine, it isnecessary to provide for an organic polymer film or oxide film as abonding (or binding) acceleration (promotion) layer. This bondingacceleration layer is required to have such properties as to be ableeasily to form a hydrate at its reaction site on the surface, to have astrong adhesion with the surface of the fuel injection valve, and to beensured to exist stably at 5-12 MPa of fuel pressures, at 150 -200° C.on the surface of the fuel injection valve, and in a stringentenvironment of gasoline combustion. As organic polymeric films that canbe used enduring such stringent environments, there are a thermo-setfilm of a ladder type silicone group origomer, an epoxy resin cured filmand the like. As oxide films, there are SiO₂, Al₂ 0 ₃, TiO₂ or the like.On either one of these bonding accelerators provided as above,perfluoropolyether compound 6-40 is reaction-bonded firmly so as toaccomplish the fuel injection valve which can eliminate the accumulationof deposits according to the invention. It should be noted, however,that when the thickness of the bonding acceleration film increasesexcessively, a strain is caused to occur between the fuel injectionvalve and the bonding acceleration film due to a difference in theirthermal expansion coefficients, thereby resulting in a peel-off of thebonding accelerator film. Therefore, the thickness of the bondingaccelerator film is preferably as thin as possible.

Specific examples of the ladder type silicone group oligomers used asthe bonding accelerator include glass resin GR100, GR650, GR908, GR950available from SHOWA DENKO, LTD. Well-known examples of such epoxyresins include Epicoat Series of Yuka Shell Epoxy KK, XD9053 of DowChemical Japan KK, and the like. As oxide films for the bondingacceleration, a baked film of various metal alkoxides, aluminum cheltereagents and the like are used. Specific examples of metal alkoxidesinclude tetraethoxysilane (SHINETSU KAGAKU KOGYO K.K.: KBE04),tetromethoxysilane (SHINETSU KAGAKU KOGYO K.K.: KBM04),tetraethoxytitane (DINAMITE NOBEL JAPAN K.K.: ET), tetramethoxytitan(DINAMITE NOBEL JAPAN K.K.: MT), tetrapthoxytitan (DINAMITE NOBEL JAPANK.K.: BT) and the like. As the alminum chelete reagent, there is alminumchelete A available from Kawa-Ken Fine Chemical K.K.

A fuel injection valve according to one aspect of the invention isprovided with at least one of the following features that an organicfilm of a 1.5 nm to 8 nm thickness is provided on the port and in thevicinity of the fuel injection port, or on the surface of the fuelinjection valve, that the fuel injection valve has an opening from 0.3mm to 0.8 mm diameter capable of atomizing fuel into particles in lessthan 20 μm in diameter, and that the fuel injection valve port and itsvicinity are manufactured using a ferrite stainless steel comprising ofC from 0.6 to 1.5%, Si less than 1%, Mn less than 1.5%, and Cr from 15to 20% by weight. The organic film which is comprised of any one of theabove-mentioned compounds is bonded with its base metal by covalentbinding, the thickness of which film is preferably 1.5-30 nm, morepreferably 1.5-10 nm, and the most preferably 1.5-7 nm.

Further, as the organic film may be formed of usingtetrafluoride-ethylene monomer by glow discharge. Other candidates ofthe organic film are Teflon resin, or a solution of metal alkoxide andfluoroalkyl group substituted alkoxide, and the like.

According to another aspect of the invention, a gasoline directinjection engine is provided, which is comprised of a cylinder headhaving air intake means and exhaust means connected to the combustionchamber, a piston reciprocating within the cylinder, fuel injectionmeans for injecting fuel into the combustion chamber, and ignition meansfor igniting atomized fuel, and wherein said fuel injection means iscomprised of the above-mentioned fuel injection valve.

According to still another aspect of the invention, a gasoline directinjection engine is provided, wherein the same is comprised of acylinder head having air intake means and exhaust means connected to thecombustion chamber, a piston reciprocating within the cylinder, fuelinjection means for injecting fuel into the combustion chamber, andignition means for igniting atomized fuel, and wherein the surfaces ofan injection port and its vicinity of said fuel injection are coatedwith an organic film.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

FIG. 1 shows a gasoline direct injection type internal combustion enginefor automobile according to one embodiment of the invention. A fuelinjection valve 1 which is mounted on a cylinder head 10 has an openingat its end portion for directly injecting fuel supplied from a fuelgallery into a combustion chamber 14.

An ignition plug 3 which is provided between an intake valve 4 and anexhaust valve 5 ignites a mixture of air and fuel to start combustion,the air being supplied from intake port 6 and through intake valve 4 bymoving of piston 8, and the fuel injected from injection valve 1. Anexhaust gas after combustion is exhausted through exhaust valve 5 bymoving of piston 8 while it is open.

An injection valve moving signal terminal 11 of fuel injection valve 1is electrically connected to a fuel injection valve moving circuit 2.Further, the fuel injection valve moving circuit 2 is electricallyconnected to an electronic control unit (ECU) 9 which emits a fuelinjection valve moving trigger signal and a signal whether or not tomove the fuel injection valve in such a manner as to minimize anoperation delay of the valve body. By way of example, ECU 9, which issupplied with data representing various operational conditions of theengine, determines a fuel injection valve moving trigger signal inresponse to the operational conditions.

An air flow from intake port 6 is controlled by electromagnetic means Mwhich is provided dually and operates with the motion of an acceleratorpedal. Hydrocarbon, carbon monoxide, and NOx, which are included in theexhaust gas after combustion, are removed by a low oxygen storage typethree-way catalyst 12 and a lean NOx catalyst 13. In this embodiment 1of the invention, a particle size of atomized fuel injected from thefuel injection valve 1 is less than 25 μm, preferably less than 15 μm,and more preferably less than 10 μm, and whereby a super lean-burn withan air fuel ratio of 50 is realized. In the three-way catalyst 12, Pt orCe is supported by alumina supports. In NOx catalyst 13, Pt is supportedby alumina supports, or oxides of Na, Ti are supported therein.

With reference to FIG. 2, a schematic view of a cross-section of fuelinjection valve 1 of the invention is shown, which is mounted in thecylinder head 10. In FIG. 2, numeral 22 depicts a housing; 23 depicts acore; 25 a coil; 26 an armature; 27 a valve unit; wherein valve unit 27is supported by one end of the housing 22 by caulked joint. Further,valve unit 27 is comprised of: a valve body 29 which is a step-wisehollow cylinder having a minor diameter cylinder portion and a majordiameter cylinder portion; a valve sheet 32 which is firmly fixed to theend of a center port inside the valve body 29, and has a fuel injectionport 31; and a needle valve 33 which is operated by a solenoid device tocontact and separate from valve sheet 32 to open and close fuelinjection port 31. Numeral 34 indicates a space in contact with a bottomsurface of the coil assembly and surrounded by the housing and the core,which more specifically corresponds to a pair of O-rings disposed on theside of fuel pressure application. Numeral 35 depicts a swirler. Adiameter of the fuel injection valve port 31 is 0.8 μm.

Now, the operation of the fuel injection valve will be described. Whencoil 25 is given an electronic signal, a magnetic flux is produced inthe magnetic circuit including armature 26, core 23 and housing 22,whereby armature 26 is attracted toward core 23, thereby separatingneedle valve 33 which is integral with armature 26 from valve sheet 32so as to provide for a gap therebetween. Then, a pressurized fuel isguided from valve body 29 through the gap into injection port 31 in thevalve sheet 32 so as to be injected therefrom as atomized particles asdescribed above.

Further, the fuel injection valve 1 is mounted so as to protrude intothe cylinder as much as 2-10 mm.

In particular, valve body 29, valve sheet 32, needle valve 33 andswirler 35 are manufactured using 1 wt % of C and 16 wt % of Crcontaining ferrite stainless steel of JIS Standard SUS44C, which iscold-processed, annealed, and machined into final shapes. The diameterof injection valve port 31 is 0.8 mm, and a roundness at its minordiameter is less than 0.5 μmm.

A method for forming a coating of perfluoropolyether compounds at theend portion of fuel injection valve 1, and its effect and advantage willbe described in the following.

Perfluoropolyether compounds such as Compound 8 having numerical averagemolecular weight of 2690, Compound 19 having numerical average molecularweight of 2190, Compound 39 having numerical average molecular weight of2302 are dissolved in perfluorohexane of FC-72 (Trade name; Sumitomo 3MK.K.) to produce a solution of 0.2 wt % concentration. The nozzle endportion of the fuel injection valve of FIG. 2 is immersed into thissolution for one hour. Then, the fuel injection valve taken out from thesolution is heated at 150° C. for 10 minutes. By this heat treatment,alkoxy silane which is a terminal functional group of perfluoropolyethercompounds of Compounds 8, 19, 37 is caused to have a dehydrationreaction with a hydroxyl group on the surface of the fuel injectionvalve, whereby the both of them undergo a covalence binding to form ahighly adhesive coating approximately of 2 nm thickness. This coating isprovided on the whole area of the internal surface of swirler 35, thewhole area of needle valve 33 corresponding to the swirler, on the valvesheet 32, on the fuel injection port 31, and on the valve body 29corresponding to the part of the swirler. The fuel injection valvesafter treatment by the perfluoropolyether compounds of 8, 19 and 37 aremounted on a test engine to observe accumulation of deposits. Gasolineflow reduction rates are measured as an index of a quantity of deposits.The test engine used is a gasoline direct injection four-cycle, V-type/6cylinder engine (Nissan Motors). Water of 80° C. is circulated in theengine head to keep the temperature of the engine head at 90-110° C.Test were conducted at engine rotation of 1200 rpm, fuel flow rate at2200 cc/h and for 40 hours of operation.

In reference to FIG. 3, a relationship between the operation time andthe decrease in the fuel flow rate is shown for respective cases of thefuel injection valve where its surface is treated by perfluoropolyethercompounds 8, 19 and 37, respectively. Comparison examples shown hereinclude non-treated one the surface of which is not treated with anyperfluoropolyether compound, and those which are treated with thefollowing fluoroalkyl compounds 41 and 42 in 0.2 wt % concentration,respectively.

C₆F₁₃—C₂H₄—Si(O—C₂H₅)₃ (molecular weight: 510)   (Comp. 41),

CF₃—C₂H₄—Si(OCH₃)₃ (molecular weight: 218)   (Comp. 42).

With reference to FIG. 3, in respective cases where the surfaces aretreated with compounds 8, 19 or 37 respectively, their fuel flowdecreasing rates are suppressed to be less than 2%, which issubstantially smaller than the cases treated with comparison examples41, 42 and the non-treated one. This result reveals that when thesurface is treated with the perfluoropolyether compounds, a flowresistance due to accumulation of deposits becomes substantially small,thereby showing an excellent effect to prevent accumulation of thedeposits.

Embodiment 2

Solutions of respective perfluoropolyether compounds 8 with numeralaverage molecule weight of 2690, 19 with numeral average molecule weightof 2190 and 37 with numeral average molecule weight of 4880 are preparedby dissolving these compounds into perfluorohexane of FC-72 (Trade name:Sumitomo 3M K.K.) in 0.01, 0.05, 0.075, 0.1 and 0.2 wt % concentrations,respectively. Into these solutions, the nozzle portion of the fuelinjection valve shown in FIG. 2 is immersed for one hour. Then, thevalve hauling up from the solution is heated at 150° C. for ten minutes.Through such heat treatment, alkoxy silane which is the terminalfunctional group of the perfluoropolyether compounds 8, 19 and 37 iscaused to have a dehydration reaction with the hydroxyl group present onthe surface of the fuel injection valve, whereby both of them areallowed to have a covalence binding to form a coating film ofapproximately 2 nm thick. The thickness of the films of theperfluoropolyether compounds firmly coated on the surface of the fuelinjection valve was measured by the reflection adsorption spectroscopy(RAS) method using an infrared spectroscopy 1720 of Perkin-Elmer. In themeasurement of thickness, spectra of 1250-1275 cm⁻¹ in stretchingvibration of C-F which is the main structure of perfluoropolyether wereused, and its absorption was converted to a film thickness. The filmthickness was calibrated using ellipsometry. A relationship betweenconcentrations of coating and film thicknesses for each of theperfluoropolyether compounds 8, 19 and 37 is shown in FIG. 4.Reaction-bonded film thicknesses of the perfluoropolyether compounds 8,19 and 37 were in the range of 0.8 nm to 6.2 nm. A fuel injection valvetreated with perfluoropolyether compound 8 was mounted on the testengine, and its deposit accumulation condition was observed. A gasolineflow reduction was measured as an index of a quantity of accumulation ofdeposits. The test engine used was a direct injection 4-cycle, V-type/6cylinder engine manufactured by Nissan Motor Co., and the temperature ofits engine head was controlled at 90-110° C. by circulating water of 80°C. in the engine head. The test was done at 1200 rpm, with a fuel flowof 2200 cc/h, and for 40 hours of operation.

With reference to FIG. 5, decreases in fuel flow rates relative to timesof operation are shown for respective cases where the perfluoropolyethercompound 8 was coated on the surface in 0.01, 0.05, 0.075, 0.1 and 0.2wt % concentrations, respectively. Film thicknesses coated were 1.0,1.3, 1.5, 2.0 and 3.7 nm, respectively, and each contact angle for wateris more than 100 degrees. Comparison examples used include non-treatedone the surface of which was not treated with any perfluoropolyethercompound, and another one the surface of which was coated with thefluoroalkyl compound of 41 in 0.2 wt % concentration. Film thicknessmeasurements of the fluoroalkyl compound were conducted using theinfrared spectroscopy type 1720 of Perkin-Elmer, and by the reflectionadsorption spectroscopy (RAS) method. In this measurements, spectra of1200 cm⁻¹ in the stretching vibration of C-F which is the main structureof the fluoroalkyl compound were used, and its film thickness wasobtained by conversion from its absorption. The film thickness wascalibrated using the ellipsometry. The thickness of compound 41 treatedwas 2.3 nm.

It is known from FIG. 5 that in the case where the surface is treatedwith compound 8 to have a film thickness of 1.5 nm or more, a decreasein its fuel flow rate is suppressed to be less than 2%, which issubstantially smaller than the cases where the surface is treated withcomparison compound 41 in a film thickness of 2.3 nm, and thenon-treated example. This result reveals that when the surface istreated with the perfluoropolyether compound 8 to have the filmthickness more than 1.5 nm, any substantial flow resistance due toaccumulation of the deposits does not occur thereby proving itsexcellent advantage and effect to be able to prevent deposition of thedeposits. Further, observation of deposit accumulation after 40 hours ofoperation on the injection port 3 of the fuel injection valve which wastreated with the perfluoropolyether compound of the invention in thethickness more than 1.5 nm revealed that its deposit accumulation wasremarkably smaller compared with the comparison examples.

Embodiment 3

Perfluoropolyether compounds of the invention: compound 8 with numeralaverage molecular weight of 2690; compound 19 with numeral averagemolecular weight of 2190; compound 37 with numeral average molecularweight of 4880; and compound 38 with numeral average molecular weight of4820, are dissolved respectively into perfluorobutylmethylether HFE7100(Trade name: Sumitomo 3M K.K.) to prepare a solution thereof in 0.2 wt %concentration. In the same manner as with the Embodiment 1, a fuelinjection valve as shown in FIG. 2 is immersed in this solution for onehour so as to form a coating comprising the perfluoropolyether compoundof the invention on the surfaces of the fuel injection valve and theinjection port. Then, the fuel injection valve unit is hauled up fromthe solution, and heated at 150° C. for ten minutes. A film thickness ofthe perfluoropolyether compound which is reaction-bonded on the fuelinjection valve was measured using the infrared spectroscopy 1720 typefrom Perkin-Elmer, and by the RAS method. Spectra of 1250-1270 cm⁻¹ inthe stretching vibration of C-F which is the main composition of theperfluoropolyether were used in the measurements, and its film thicknessis obtained by conversion from its absorption. The film thickness iscalibrated using the elliptometry. Film thicknesses reaction-bonded onthe surface of the fuel injection valve are 3.6 nm for the compound 8,3.2 nm for the compound 19, 5.8 nm for the compound 37, and 5.9 nm forthe compound 38, respectively. Contact angles for water are more than100 degrees, respectively.

In addition, comparison examples were prepared using the followingfluoroalkyl compounds of compounds 41-46, as well as perfluoropolyethercompounds of compounds 45, 46, which are dissolved intoperfluorobutylmethylether HFE7100 (Trade Name of Sumitomo 3M K.K.) toproduce each solution thereof in 0.5 wt % concentration. Into thissolution, the nozzle end portion of a fuel injection valve as shown inFIG. 2 is immersed for one hour. Then, the same is hauled up from thesolution, and heated at 150° C. for ten minutes. In this manner thecoating thereof is reaction-bonded on the fuel injection valve.Molecular weights of compounds 41-46 are 510, 218, 390, 610, 1860 and1530, respectively. Film thicknesses of reaction-bonded compounds boundon the surface of the fuel injection valve are 18.9 nm with compound 41,38.2 nm with compound 42, 32.8 nm with compound 43, 10.8 nm withcompound 44, 42.6 nm with compound 45, and 40.2 nm with compound 46,respectively. Contact angles for water were more than 100 degrees forall cases.

Compound 43:

(CF₃)₂CFO—C₃H₆—Si(OC₂H₅)₃

(molecular weight: 390)

Compound 44:

F(CF₂)₈—C₂H₄—Si(OC₂H₅)₃

(molecular weight: 610)

Compound 45:

F(—CF₂—CF₂—CF₂—O—)_(m)—C₂F₄—CONH—C₃H₆—Si(OC₂H₅)₃

(m=9 in average)

(average molecular weight: 8160)

Compound 46:

F(—CF(CF₃)—CF₂—O—)_(m)—CF(CF₃)—CONH—C₃H₆—Si(O—C₂H₅)₃

(m=7 in average)

(average molecular weight: 1530).

The fuel injection valves the surface of which are treated with eitherof the perfluoropolyether compounds of 8, 9, 37 and 38, the fluoroalkylcompounds of 41-44, and the perfluoropolyether compounds of 45 and 46according to the invention were mounted on the test engine to observethe state of accumulation of the deposits and to measure respectivedecreases in the fuel flow rates as indices representing a quantity ofthe deposits accumulated. The test engine used is a direct injection4-cycle, V-type/6 cylinder engine manufactured by Nissan Motors Co.Water is circulated at 80° C. through the engine head to keep thetemperature of the engine head at 90-110° C. The test was done at 1200rpm, and the fuel flow rate at 2200 cc/h. The test duration time was setfor 140 hours.

With reference to FIG. 6, when the perfluoropolyether compound havingnumeral average molecular weight greater than 2190 is reaction-bonded onthe surface in a thickness of 2.3 nm or more, the decrease in the fuelflow rate is confirmed to be suppressed less than 2%, which isremarkably smaller than the cases where the surface is treated with thefluoroalkyl compounds of the comparison examples having molecularweights of 218-610 with 10.8-38.2 nm thickness. Further, in the case ofthe perfluoropolyether compounds having a molecular weight less than1860, even if its film thickness is thick as 40.2 or 42.6 nm, thedecrease in the flow rate due to occurrence of the deposits is observedto become 3-5%. Although its effect is recognized, the effect is notsufficient. It is concluded from the result of the tests that in thecase where the perfluoropolyether compound having a numeral averagemolecular weight greater than 2190 is used, a film thickness of 1.5 nmor more can adequately prevent accumulation of the deposits, however,that in the case where the fluoroalkyl compound with a smaller molecularweight is used, even if its film thickness is given sufficiently thick,a substantial occurrence of the deposits cannot be prevented. Further,with the perfluoropolyether compounds having molecular weights of 1530and 1860, a sufficient effect could not have been obtained.

Embodiment 4

A solution of glass resin GR100 manufactured by Showa-Denko Co. isprepared by dissolving the same into methyl ethyl keton in 0.02 wt %concentration. Into this solution, a fuel injection valve the leadingend of which is chrome-plated is immersed so as to coat the surfaces ofthe fuel injection valve and the injection port with glass resin GR100.Then, the fuel injection valve is hauled up from the solution, heated at200° C. for 30 minutes, thereby baking the coating of glass resin GR100on the surfaces of the fuel injection valve and its injection port.Then, compound 6 having a molecular weight of 2670 is dissolved intoperfluorobutylmethylether HFE7100 (Trade Name of Sumitomo 3M K.K.) toproduce a solution thereof with 0.2wt % concentration. Theabove-mentioned fuel injection valve which is baked on its surface withthe coating of glass resin GR100 is immersed into this solution for onehour. Then, the fuel injection valve, after hauling up from the solutionis heated at 150° C. for ten minutes. In this manner, thin layers ofglass resin GR100 and the compound 6 are formed on the surfaces of thefuel injection valve and its internal injection port. A film thicknessof the compound 6 was 3.2 nm and a contact angle for water on thesurface of the fuel injection valve was greater than 100 degrees.

As a comparison example, a fuel injection valve the end portion of whichis chrome-plated is immersed in the solution of compound 6 with 0.2 wt %concentration thereof (solvent used: perfluorobutylmethylether HFE7100(trade name of Sumitomo 3M K.K.)) for one hour, after hauling up fromthe solution, heated at 150° C. for ten minutes. A film thickness of thecomparison example using compound 6 was measured using the RAS method tobe 1.1 thick. A contact angle for water is less than 100 degrees. Thisfuel injection valve was mounted on the test engine, and a state ofaccumulation of the deposits thereon was observed, and measurements ofthe decreases in the fuel flow rates as an index which represents aquantity of deposits were conducted. The engine used for evaluation ofthe state of accumulation of the deposits is the direct injection4-cycle, V-type/6-cylinder engine manufactured by Nissan Motors Co.Water is circulated through the engine head at 80° C. to maintain thetemperature of the engine head from 90-110° C. The tests were done at1200 rpm, 2200 cc/h of a fuel flow rate, and for 140 hours of operation.

In reference to FIG. 7, the fuel injection valve the end portion ofwhich is chrome-plated, and coated with both the layers of glass resinGR100 and compound 6 in combination features a thicker film layer ofcompound 6 compared with the comparison example the end portion of whichis chrome-plated and coated with the layer of compound 6 alone, and aremarkably smaller decrease in the flow reduction rates. From thisresult, it is concluded that the organic polymeric layer of glass resinGR100 is very effective as the bonding acceleration layer.

Embodiment 5

A solution [A] is prepared by dissolving 0.44 g of epoxy resin EP1004(Yuka Shell Epoxy K.K.), 0.30 g of Malkalineka-M (Maruzen-Sekiyu-KagakuK.K.) which is polyp-hydroxy-styrene resin, and 0.004 g oftriethylammoniumborate TEA-K (Hokko-kagagu K.K.) which is a hardeningaccelerator, into a mixture solvent of 95 g of methyl ethyl keton and 5g of 2-butoxyethyl acetate. A fuel injection valve the end portion ofwhich is chrome-plated is immersed in this solution [A] to provide for acoating of solution [A] on the surface of the fuel injection valve andon the internal wall of the injection port thereof. Then, the fuelinjection valve is hauled up from the solution, heated at 200° C. for 30minutes, so as to bake the layer of film comprising solution [A] on thesurface of the injection valve and on the internal wall of the injectionport thereof. Nextly, a solution of compound 6 having a molecular weightof 2670 is prepared by dissolving into perfluorobutylmethylether HFE7100(Sumitomo 3M K.K.) with 0.2 wt % concentration thereof. Into thissolution, the above-mentioned fuel injection valve the end portion ofwhich is baked with the coating comprising solution [A] is immersed forone hour. Then, the fuel injection valve after hauling up from thesolution is heated at 150° C. for ten minutes. In this way, thin layersof coating of glass resin GR100 and compound 6 are formed on the surfaceof the fuel injection valve and on the internal wall of the injectionport thereof. A film thickness of compound 6 was 3.5 nm, and a contactangle for water on the surface of the fuel injection valve was more than100 degrees.

A comparison example was prepared by immersing a fuel injection valvethe leading edge portion of which was chrome-plated into a solution ofcompound 6 with 0.2 wt % concentration (solvent:perfluorobutylmethylether HFE7100 (Sumitomo 3M K.K.)) for one hour, thenthe same was hauled up from the solution, heated at 150° C. for tenminutes. A film thickness of compound 6 for the comparison example wasmeasured using the RAS method to be 1.0 nm thick. Its contact angle forwater is less than 100 degrees. This fuel injection valve was mounted onthe test engine, and conditions of accumulation of deposits wereobserved, and decreases in the fuel flow rates, which are indicesindicative of a quantity of accumulation of the deposits were measured.The test engine used in the evaluation of accumulation of the depositsis the direct injection 4-cycle, V-type 6-cylinder engine manufacturedby Nissan Motors Co. Water is circulated through the engine head at 80°C. to keep the temperature of the engine head at 90-110° C. The testswere done at 1200 rpm, at 2200 cc/h of fuel flow rate, and for 140 hoursof operation.

As clearly shown in FIG. 8, the fuel injection valve the leading portionof which was chrome-plated, and coated with both layers of solution [A]and compound 6 is characterized by having a thicker coating of compound6 and having an extremely smaller decrease in the flow reduction ratescompared with another fuel injection valve which is chrome-plated andcoated with compound 6 alone. From this result, it is concluded that theorganic polymer layer of the invention is very effective as the bondingacceleration layer.

Embodiment 6

A solution of tetraethoxy silane KBE04 (Shinetsu Kagagu-kogyo K.K.) of0.05 wt% concentration was prepared by dissolving into methanol. Intothis solution, a fuel injection nozzle the leading edge of which waschrome-plated was immersed. After hauling up from the solution, the fuelinjection valve was heated at 250° C. for one hour to form a SiO₂ filmon the surface of the fuel injection valve. Nextly, a solution ofcompound 26 with molecular weight of 4280 and of 0.2 wt % concentrationwas prepared by dissolving the same into perfluorobutylmethyletherHFE7100 (Trade Name of Sumitomo 3M K.K.). The above-mentioned fuelinjection valve on the surface of which the SiO₂ film was formed wasimmersed into this solution of compound 26 for one hour. Then, aftertaking out of the solution, the fuel injection valve is heated at 150°C. for ten minutes. In this way, thin films of oxides of tetraethoxysilane and of compound 26 were formed on the surface of the fuelinjection valve and on the internal wall of the injection port thereof.A film thickness of compound 26 was measured using the RAS method to be2.8 nm. A contact angle for water was greater than 100 degrees.

A comparison example was prepared by immersing a fuel injection valve,the leading edge of which was chrome-plated, into a solution of compound26 of 0.2 wt % concentration (which uses a solvent ofperfluorobutylmethylether HFE7100 of Sumitomo 3M K.K.) for one hour,then the fuel injection valve having been hauled up from the solutionwas heated at 150° C. for ten minutes. A film thickness of compound 26of the comparison example was measured by the RAS method and found outto be 0.9 nm. A contact angle for water was less than 100 degrees. Thisfuel injection valve was mounted on the test engine to monitor thecondition of accumulation of deposits and to measure a decrease in thegasoline flow rate as an index representing a quantity of depositsthereon. The test engine used was a direct injection 4-cycle, V-type6-cylinder engine manufactured by Nissan Motors Co. By circulating waterat 80° C. through the engine head, the temperature of the engine headwas controlled at 90-110° C. The tests were done at 1200 rpm, 2200 cc/hof fuel flow, and for 140 hours of operation.

As clearly shown in FIG. 9, the fuel injection valve the leading edgeportion of which was chrome-plated and coated by layers of both thetetraethoxy silane oxide and the compound 26 has a thicker film ofcompound 26 compared to the comparison fuel injection valve the edgeportion of which was chrome-plated and coated by compound 26 alone, andthereby having a remarkably smaller decrease in the flow rate. From thisresult, it is concluded that the oxide film of the invention is veryeffective as the bonding acceleration layer.

Embodiment 7

A solution of aluminum chelete A (Kawaken Fine Chemical K.K.) of 0.05 wt% concentration was prepared by dissolving into methanol. Into thissolution, a fuel injection valve the edge portion of which waschrome-plated is immersed. After hauling up from the solution, this fuelinjection valve is heated at 250° C. for one hour to form a film ofAl₂O₃ on the surface thereof. Then, a solution of compound 37 withmolecular weight of 4880 and in 0.2 wt % concentration is prepared bydissolving into perfluorobutylmethylether HFE7100 (Trade Name ofSumitomo 3M K.K.). Into this solution, the above-mentioned fuelinjection valve coated with Al₂O₃ on the surface thereof is immersed forone hour. Then, after hauling up from the solution, the fuel injectionvalve is heated at 150° C. for ten minutes. In this way, both layers ofa thin A ₂ 0 ₃ film and compound 37 are formed on the surface of thefuel injection valve and on the internal wall of the injection portthereof. A film thickness of compound 37 was measured using the RASmethod and found out to be 3.2 nm thick. A contact angle for water wasgreater than 100 degrees.

A comparison example is prepared by immersing a fuel injection valve theedge portion of which was chrome-plated into a solution of compound 37with 0.2 wt % concentration (which uses as its solventperfluorobutylmethylether HFE7100 (Sumitomo 3M K.K.)) for one hour, andafter taking out of the solution, heating at 150° C. for ten minutes. Afilm thickness of compound 37 on the comparison example was measuredusing the RAS method to be 0.9 nm. A contact angle for water is smallerthan 100 degrees. These fuel injection valves were mounted on the testengine, and conditions of accumulation of deposits were monitored, andalso measurements of decreases in the gasoline flow rates as indexesrepresenting quantities of accumulation of deposits were conducted. Thetest engine used for evaluation of the conditions of accumulation ofdeposits is a direct injection 4-cycle, V-type 6-cylinder enginemanufactured by Nissan Motors Co. By circulating water at 80° C. throughthe engine head, the temperature of the engine head was controlled at90-110° C. The tests were done at 1200 rpm, 2200 cc/h fuel rate, and for140 hours of operation.

As clearly shown in FIG. 10, the fuel injection valve the edge portionof which was chrome-plated and coated by both layers of Al₂O₃ film andcompound 37 is characterized by having a thicker film of compound 37compared to the comparison example which was chrome-plated and coated bycompound 37 alone, thereby advantageously having a remarkably smallerdecrease in the flow reduction rates. From the result, it can beconcluded that the oxide film of the invention is very effective as thebonding acceleration layer.

Embodiment 8

With reference to FIG. 11, a schematic block diagram of a directinjection engine according to another embodiment of the invention isshown. Embodiment 8 of the invention is comprised of: an air intakesensor 49; a throttle actuator 40; an ignition plug 48; a high pressurefuel injection valve 47 for directly injecting atomized fuel particlesinto a cylinder suitable of super lean burn combustion as in theembodiment 1; a high pressure fuel supply pump 51 for supplying fuel tothe high pressure injection valve; an air/fuel ratio sensor 41; acatalyst 42; and a control unit 43, wherein the feature of the inventionis characterized in a control method of the control unit 43 in anarrangement of the invention in which the high pressure injection valve47 is provided in juxtaposition with ignition plug 48. The control unit43 determines a combustion mode in response to an acceleration pedaloperation and an engine speed by its combustion mode determinationmeans. After calculation of a target air/fuel ratio by a target air/fuelratio computing means in response to a combustion mode, a fuel injectionquantity is computed by a fuel injection computing means. On the otherhand, a throttle opening value is calculated by a throttle opening valuecomputing means in response to the combustion mode.

With respect to numerals in FIG. 11, 46 depicts an air intake valve, 45depicts a piston, 50 depicts an exhaust valve. Fuel injection valve 47used here is the same as that of embodiment 1 as shown in FIG. 2, and adeposit accumulation prevention film of the invention is formed on itspart and vicinity thereof to be exposed to a combustion gas, then,engine tests thereof were conducted in the same way as the otherembodiments of the invention. A film thickness of its depositionprevention coating was set at approximately 2 nm. A flow reduction rateafter 40 hours of operation for this embodiment was measured, and itsflow reduction rate was found to be extremely small as small as 2%.

The following features have been accomplished according to the inventionthat the accumulation of deposits on the surface of the gasoline directinjection valve during combustion of gasoline can be prevented, and/or agasoline direct injection valve which can easily remove the depositsaccumulated thereon is provided, thereby ensuring optimization of agasoline concentration and air flow specified in the engine cylinder fora long time of operation, enabling the super lean burn combustioncontrol, and thereby providing automobiles with improved fuel mileage.

What is claimed is:
 1. A fuel injection valve coated with an organiclayer of film on the surface of its fuel injection port, wherein saidorganic film of layer comprises a perfluoropolyether compound having amolecular weight of 2000 to 6000 in average.
 2. A fuel injection valveaccording to claim 1, wherein said layer of perfluoropolyether compoundhas a thickness in a range from 1.5 nm to 30 nm.
 3. A fuel injectionvalve according to claim 1, which coating has a thickness in a rangefrom 1.5 nm to 30 nm, on the surface of its fuel injection port and itsvicinity.
 4. A fuel injection valve according to claim 3, wherein athickness of said layer is 1.5 nm to 10 nm.
 5. A fuel injection valveaccording to claim 1, wherein the organic film is coated on a surface ofthe valve fuel injection port which has a nozzle capable of atomizingfuel into a particle size of 20 μm or less.
 6. A fuel injection valveaccording to claim 1, wherein the organic film is coated on the surfaceof its fuel injection port which has a diameter of 0.3-0.8 mm.
 7. A fuelinjection valve according to claim 1, wherein the organic film is coatedon a surface of the valve fuel injection port which, along with aportion in the vicinity thereof, comprise a ferrite stainless steelhaving 0.6-1.5 wt % of C, 1 wt % or less of Si, 1.5 wt % or less of Mnand 15-20 wt % of Cr.
 8. A fuel injection valve having an organic filmcoating having a thickness in a range from 1.5 nm to 30 nm, on thesurface of its fuel injection port and its vicinity, wherein saidorganic coating of film comprises one of perfluoropolyether compounds ofthe following compounds 1 and 2 which has an average molecular weightfrom 2000 to 6000, F—(C_(x)F_(2x)O)_(n)—A orA—{(C_(x)F_(2x)O)_(n)}—A,  (Comp. 1) F—(C_(x)F_(2x)O)_(n)—C₂F₄—B orB—{(C_(x)F_(2x)O)_(n)}—B,  (Comp. 2) and wherein X is an integer from 1to 3 which may differ upon repetition, n is a value at which a numericaverage molecular weight of —(C_(x)F_(2x)O)_(n)— becomes 2000 or more, Ais a residue, and B is a residue of alkoxy silane group.
 9. Means forpreventing gasoline combustion deposits from settling on a surface of afuel injection valve of a direct injection engine, comprising coatingthe surface of the fuel injection valve with a perfluoropolyethercompound having an average molecular weight of 2000 to
 6000. 10. A fuelinjection valve coated with an organic layer of film on the surface ofits fuel injection port, wherein said organic film of layer comprises aperfluoropolyether compound as defined in the following chemicalcompound 1, F—(C_(X)F_(2X)O)_(n)—A orA—{(C_(x)F_(2x)O)_(n)}—A,  (Comp. 1) wherein X is an integer from 1 to 3which may differ upon repetition, n is a value at which a numericaverage molecular weight of —(C_(X)F_(2X)O)_(n)— becomes 2000 or more,and A is a residue.
 11. A fuel injection value coated with an organiclayer of film on the surface of its fuel injection port, wherein saidorganic layer of film comprises a perfluoropolyether compound as definedin the following chemical compound 2 F—(C_(X)F_(2X)O)_(n)—C₂F₄—B orB—{(C_(x)F_(2x)O)_(n)}—B,  (Comp. 2) wherein X is an integer from 1 to 3which may differ upon repetition, n is a value at which a numericaverage molecular weight of —(C_(X)F_(2X)O)_(n)— becomes 2000 or more,and B is a residue of alkoxy silane group.
 12. A fuel injection valvecoated with an organic layer of film on the surface of its fuelinjection port, wherein said organic layer of film comprises forming alayer of perfluoropolyether compounds 1 or 2 on the surface thereof viaa bonding acceleration layer which is an organic polymer film or anoxide film, wherein F—(C_(X)F_(2X)O)_(n)—A orA—{(C_(x)F_(2x)O)_(n)}—A,  (Comp. 1) F—(C_(X)F_(2X)O)_(n)—C₂F₄—B orB—{(C_(x)F_(2x)O)_(n)}—B,  (Comp. 2) and wherein X is an integer from 1to 3 which may differ upon repetition, n is a value at which a numericaverage molecular weight of —(C_(X)F_(2X)O)_(n)— becomes 2000 or more, Ais a residue, and B is a residue of alkoxy silane group.